The Global Energy Problem
The ability to harness the stored energy of fossil fuels in the form of electricity has enabled humans to make amazing advances toward our wellbeing. However, as the global demand for electricity continues to increase, it is widely anticipated that the resulting impact on the environment will ultimately reach a point where it becomes a threat to our survival. Therefore, resolving the constraints to universal access to electricity without unsustainable environmental consequence is a social and economic priority of the highest order.
To meet the legitimate aspirations of the world's population and impact poverty, the US Energy Information Administration estimates an increase of over 50% in global energy requirements by 2040 (Reference: International Energy Outlook 2016). At the same time, a significant decrease in environmental impact and cost of energy is required. Our traditional power generation methods use fossil fuels that are all constrained resources. At present, our only proven clean generation options are hydro, geothermal, biomass, solar and wind. Of these, solar and wind present the best opportunity to meet our future needs, as the others have very specific geographic inputs and requirements.
The global consensus of policymakers is that we need to dramatically increase our clean energy generation, as evidenced by the recent Paris Climate or COP21 agreement. However, with our current and forecast advances in clean generation technology, the design of our electricity networks is incapable of allowing us to achieve the mandated goals. In particular, integration is a well-known and unsolved issue.
Electricity System Overview
The entire electricity supply chain can be generally grouped into three areas: generation, distribution, and consumption. In order to maintain a reliable power supply, energy generation is controlled to meet consumption through an end-to-end network.
Electricity distribution networks are the largest manmade objects ever created. To date, they have all been conceived and constructed for very specific operating conditions under a single design schematic. The design schematic is relatively simple: generation in the past was easily and adequately equilibrated with consumption. A small number of dispatchable generation sources supplied a series of tranched or grouped consumers. The topology of electrical networks tends to be a mixture of radial (a single large generator with consumers progressively tranched in a tree structure around it), and more complex and redundant path network topologies such as mesh and ring topologies. These topologies are designed to provide a good balance of reliability and cost based on the network demands of a few large stable and dispatchable generators and many consumers.
At present, the vast majority of electricity generation is directly controllable as it is produced from fossil fuels. The table below outlines the current makeup of electricity generation for the US and UK.
TABLE 1Percentage of Total Electricity Generation by Source (2015)US33%33%20%8%5%UK23%30%21%11%14%
As the level of variable renewable energy generation increases, our ability to control the supply of electricity to match demand becomes increasingly difficult. If this balance of supply and demand is not maintained, the stability and availability of electricity is threatened.
As the makeup of generation is changing toward more renewable energy, the characteristics of the electricity supply are changing, both the physical architecture of the network and our ability to control generation levels. This causes increasing issues of stability and efficiency, with the threshold capability of current electricity network architecture falling far short of required levels to meet our climate change targets. Attempting to resolve the situation through control of generation and/or consumption alone has intolerable social, economic and environmental effects. The configuration of the electricity distribution network needs to adapt if our electricity supply chain is to remain viable and deliver on our social and economic intentions.
Electricity System Balancing Requirement
Maintaining a reliable electricity supply requires the voltage and frequency of the grid to be maintained within a narrow band of about +/−1%. Other than the limited storage options currently available, electricity must be consumed when it is generated, and consequently supply and demand must be balanced to maintain the required target voltage and frequency. Until now, this has been accomplished by monitoring the grid at a coarse high level, and then adjusting the output of controllable generation sources that are largely fossil fuel, nuclear or hydro-electric.
Balancing of the grid can be categorised into three response times:                Long Term (days to weeks)        Medium Term (hours)        Short Term (milliseconds to minutes)        
The UN report ‘Global Trends in Renewable Energy Investment 2016’ states there are currently four potential balancing options, with an unacceptable fifth currently also being utilised globally.
In the case where demand exceeds supply:                i. Increasing the amount of faster responding conventional generation i.e. gas, coal or diesel;        ii. Interconnectors to transport electricity from one grid to another; and        iii. Demand response by paying larger industrial and commercial consumers to reduce usage when supply is falling short of demand.        
In the case where supply exceeds demand:                iv. Energy storage to store excess electricity when it is available and release it back into the grid when required; and        v. Curtailment of renewable energy generation to directly reduce supply        
A combination of these solutions in parallel would be plausible to attempt to manage the long and medium term balancing of grids. Currently, each option either has prohibitive costs, unacceptable consequences, or both.
For the short term response (milliseconds to minutes) of balancing of our grids, none of these options will successfully allow the increased penetration and consumption of renewable generation whilst maintaining a reliable power supply, for at least the reasons discussed below.
Short Term Grid Balancing Issues
The following outlines the issues that must be overcome in relation to renewable energy integration into the grid.
System Frequency
All generators inject power into our grid as alternating current (AC), and are synchronised to operate at the same frequency and phase. The amount of power injected by each generator is balanced through the ratio of its power output rating compared to all other generators injecting power into the system in order to evenly distribute the load. This occurs naturally unless modified by operator control.
Traditional fossil fuels, nuclear and even hydro power are all synchronous generators which introduce inertia to help maintain this frequency, and are controllable, providing frequency response and stability. They remain synchronised due to the self-regulating properties of their interconnection. If one generator deviates from its synchronous speed, power is transferred from the other generators in the system in such a way as to reduce the speed deviation. The stored inertial energy of the generators provides a short-term counteraction to frequency change, with governors taking over after a few seconds.
In contrast, wind and Solar Generation use significantly different technologies, producing DC power and injecting it into the AC grid through converters. This means that they are decoupled from the grid frequency, and results in asynchronous operation with no inertial energy to contribute. It is possible for converters equipped with governor-like controls to respond to frequency drops, however this cannot occur fast enough to adequately compensate and maintain grid stability. It can also only occur when the generation source is operating in a curtailed condition.
Grid Architecture
Our electricity grids have been specifically designed to deliver a reliable electricity supply from power sources through a transmission network over a long distance to load centres on a distribution network. The entire ontology of our grids is changing due to the local and dispersed nature of renewable energy generation. Our current grid hardware is incapable of adequately distributing these new power sources bi-directionally and both vertically and horizontally through the network, causing a myriad of power engineering problems, including a reduction in the capacity of the network.
Current methods for addressing these issues primarily involve additional hardware and software systems to mitigate undesired effects. These technologies are generally accepted as increasing network fragility and cost without addressing the root cause.
Control
Renewable energies such as wind and solar are not dispatchable like traditional fossil fuels, nuclear or hydro power. As we do not have control over the energy input (i.e. the wind or the sun), we are unable to ramp up or down as required to balance the system, or maintain a steady state of output. We can only actively manage the output to maintain the required power level through storage solutions or by curtailing the generation. However, curtailment is pure waste.
Variability
The rate at which the power output of renewable energies such as wind and solar can change is much faster than traditional generation technology. This occurs in two major forms:                Intermittence—renewable energy sources have long periods of unavailability due to input requirements outside of direct control (i.e. sunlight and wind).        Volatility—at all times constant variation in the output from renewable energy generation is occurring. The two main constituents of this are the rapid rate of change of output generation, and the noise inherent to the output signal.        
The law of averages helps in part to mitigate the instantaneous effects of volatility with the vast number of solar and wind generation sources. However, maintaining voltage and frequency in the short term (milliseconds to seconds) remains a significant unresolved challenge. Currently available responsive dispatchable generation technology is still significantly slower to react than the rate of change introduced by volatile renewable generation. There is no current solution to this issue.
Efficiency
Electricity grids are designed to work at a specific operating point, with a narrow band of operation due to consumption requirements. When the voltage or frequency deviates from the optimal point, the efficiency of the grid and its devices decreases, resulting in greater energy losses. Energy losses in developed grids are 5%-10%, with up to half of this loss due to non-fixed inefficiency losses. When the voltage or frequency goes outside the set operating boundaries, system protection actions are automatically undertaken which leads to both brown outs and black outs for hardware protection and safety.
Network Hardware
Electric power networks around the world use predominantly AC (alternating current) transmission and distribution. DC (direct current) is typically only used for high capacity and long distance interconnectors between separate networks (e.g. undersea cable connections). Network voltages (and sometimes frequency) must be altered at different locations to minimise transmission and distribution losses, and deliver power to consumers at manageable levels. These voltages and the resulting power flows are managed with the following devices which are designed to operate most efficiently at a fixed maximum capacity with minimum variations in demand or supply:
Circuit Breakers
Allows substations to be disconnected from the transmission network or for distribution lines to be disconnected.
Transformers
These are used for most voltage conversion duties in AC electrical power networks. Transformers are passive devices; they operate using simple electromagnetic circuit principles without any active modulation or switching schemes. Simple tap-changers are used on some transformers to regulate network voltage in discrete steps within relatively narrow ranges according to varying demand. Transformers can also transfer power bi-directionally depending upon the balance of generation and load on each side of the device.
Rectifiers
These perform direct conversion from AC to DC electrical power using semiconductor diodes or similar devices. These are also passive systems in the sense that there is no inherent switching or control capability built into their design. Large scale rectifiers are used for HV DC transmission.
Frequency Converters
These are more sophisticated devices which use active high-speed electronic switching of the mains supply to deliver frequency conversion between two different parts of the network. They range in size from small domestic network-connected solar panel inverters up to long distance HV DC to AC converters.
Power Correction Devices
There are a number of devices with the sole purpose of undertaking corrective actions on the power in the system to maintain a steady and clean power supply for use. This group of devices include but are not limited to filters, capacitors, and inductors.
Network Limitation
Increasing penetration of variable and non-dispatchable electricity generation sources (i.e. renewable energy sources such as wind and solar) are changing both the physical architecture of the network and our ability to control generation levels. This causes increasing issues of stability and efficiency, with the threshold capability of current electricity network architecture falling far short of required levels.
A New Approach to Existing Electricity Networks
It is unanimously agreed that our current electricity transmission and distribution networks are unable to provide a usable power supply above a certain threshold penetration of clean energy from wind and solar. This threshold point varies for each network based on physical architecture, generation and load profiles, as well as a myriad of other factors.
The design architecture and technology that our electricity networks use has significantly improved in cost and efficiency over the last 120 years. Yet it still utilises the same fundamental technology and design architecture that were established in the 19th Century.
One of the fundamental underpinnings of the entire electricity system, the transformer, is a passive device that is unable to effectively deal with the variability that is being imposed on its operations. For example, a transformer is exceedingly efficient at its designed operating point, but its efficiency deteriorates rapidly away from this point. A device with the capability to accept a much wider range of operating conditions with efficiency is required. The added ability to actively control operations and affect power flow through the system allows further stability and security to be delivered. This requirement is further exacerbated by the geographic distribution of new variable renewable generation being added to the existing rigid system.
All currently proposed options to upgrade our networks rely on existing operating methodologies, technologies and systems. In the case of energy storage, the technology to make this economically feasible has not yet been invented. All these options add significant cost, complexity and fragility into the network and reduce its efficiency.
It is desired to alleviate one or more difficulties of the prior art, or to at least provide a useful alternative.